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SubjectRe: SIGSEGV when using "perf record -g" with 3.13-rc* kernel
On 01/10/2014 03:06 PM, Peter Zijlstra wrote:
>
> :-)
>
> Something like this perhaps?
>
> ---
> Subject: x86, mm: Allow double faults from interrupts
>
> Waiman managed to trigger a PMI while in a emulate_vsyscall() fault, the
> PMI in turn managed to trigger a fault while obtaining a stack trace.
> This triggered the double fault logic and killed the process dead.
>
> Fix this by explicitly excluding interrupts from the double fault logic.
>
> Reported-by: Waiman Long<waiman.long@hp.com>
> Signed-off-by: Peter Zijlstra<peterz@infradead.org>
> ---
> arch/x86/mm/fault.c | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
>
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 9ff85bb8dd69..4c8e32986aad 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -641,6 +641,20 @@ no_context(struct pt_regs *regs, unsigned long error_code,
>
> /* Are we prepared to handle this kernel fault? */
> if (fixup_exception(regs)) {
> + /*
> + * Any interrupt that takes a fault gets the fixup. This
> + * makes the below double fault logic only apply to a
> + * task double faulting from task context.
> + */
> + if (in_interrupt())
> + return;
> +
> + /*
> + * Per the above we're !in_interrupt(), aka. task context.
> + *
> + * In this case we need to make sure we're not double faulting
> + * through the emulate_vsyscall() logic.
> + */
> if (current_thread_info()->sig_on_uaccess_error&& signal) {
> tsk->thread.trap_nr = X86_TRAP_PF;
> tsk->thread.error_code = error_code | PF_USER;
> @@ -649,6 +663,10 @@ no_context(struct pt_regs *regs, unsigned long error_code,
> /* XXX: hwpoison faults will set the wrong code. */
> force_sig_info_fault(signal, si_code, address, tsk, 0);
> }
> +
> + /*
> + * Barring that, we can do the fixup and be happy.
> + */
> return;
> }
>

Are you going to send out an official patch to fix this problem? I
really like to see it merged into 3.13 before it is released.

-Longman


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